This invention relates to a sandwich panel comprising
A. a core layer of polypropylene particle foam,
B. cover layers of fiber-reinforced polypropylene and also optionally
C. decorative layers.
Such sandwich panels are known, for example from DE-A 195 44 451. They are used for producing motor vehicle parts. Motor vehicle part production by stamping produces appreciable waste. It is an object of the present invention to recycle this waste.
We have found that this object is achieved, surprisingly, when the comminuted waste is added in amounts from 1 to 30% by weight in the production of foam panels from which new sandwich panels can be produced with only insignificantly inferior mechanical properties.
The present invention accordingly provides a sandwich panel as claimed in claim 1. The invention further provides a process for producing a foam panel as claimed in claim 5.
The polypropylene of the particle foam of the core layer can be a homopolymer or a copolymer with from 0.5 to 15% by weight of ethene and/or 1-butene. Its crystallite melting point is generally in the range from 120xc2x0 to 170xc2x0 C. The foam particles are produced by impregnating polypropylene minipellets with a volatile blowing agent in aqueous suspension and foaming by expansion. Foam extrusion is also possible. The particle size is customarily in the range from 2 to 8 mm, the bulk density in the range from 10 to 100 g/l.
The polypropylene of the cover layers is a homopolymer or a (graft) copolymer with maleic anhydride or acrylic acid. The cover layers preferably include from 10 to 60% by weight of glass, natural or polymeric fibers in the form of mats, nonwoven scrims, wovens or short fibers. Preference is given to glass mat reinforced polypropylene having a fiber content of from 20 to 50% by weight.
The decorative panels comprise a fiber web composed of polyester or polyamide, polymeric films or a foam film optionally laminated with a film. They may also be colored.